Inkanta ... I suspect, this is all part of the usual EU negotiating 'dance'; one side wants a full negotiation, the other says no negotiation, and they sit around a table of 28 and 'orse trade.
As Ukippers and Tory back benchers will tell you, Cameron is (as am I) a pro a lean, mean, EU bureaucratic machine, along the Founding common market lines, and he neither has the ability (with a minority party government) or will , to take an early bath and then 'pull the plug' on the EU.
The 'one sized fits all' currency and interest rate was NEVER going to work with so many countries with such different/diverse economies, just think of the UK, where we could often argue for a different north - south Uk Base Rate.
So as the U.S. found (if memory serves, taking 3 attempts to get a currency UNITED States of America) it was never going to be a simple union and likely to come apart at the first major recession.
Typically, the EU wonks solution is CLOSER union, that is their direction of travel, and the on-going question will be, on a 2 or maybe 3 speed Europe - with the original die hards in the first, with a 'mix 'n match' menu for the 2nd and 3rd speeds - does the UK still have a future within.
On a 2-3 speed solution, there will HAVE to be concessions on immigration/freedom of movement anyway, so why leave it?